Flexible Display Substrate Coating for Crack and Moisture Protection
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Solution Overview
Problem
Flexible substrates in display devices experience stress-induced defects like cracks when bent, leading to water infiltration and degradation of display elements, as the thin films on top do not always match the substrate's flexibility, causing reliability issues.
Innovation Solution
A display device design featuring a flexible first substrate with a curved part, where an organic film covers both surfaces of the substrate, including the curved region, to prevent exposure of defects and using a support member with notches to control bending, and employing a polychloropyroxyline organic film with high moisture resistance to protect the wiring and insulation layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a flexible substrate is bent to enable curvature, then the substrate can achieve desired shape and flexibility, but stress is applied to thin films arranged above the substrate causing defects such as cracks
Solution Approach 1:
The device is divided into a flexible substrate portion and a rigid circuit board portion, with the flexible substrate specifically designed to be bent into a curved shape while the rigid circuit board remains flat. This segmentation allows the flexible substrate to achieve the desired curved shape without compromising the integrity of thin films on the rigid portion.
Solution Approach 2:
Different portions of the device are assigned different mechanical properties: the substrate is made flexible to enable bending, while the circuit board is made rigid to maintain structural integrity and protect thin films. This local differentiation of mechanical properties allows the system to simultaneously achieve flexibility where needed and reliability where thin films are present.
2Strength
If thin films such as inorganic insulation films are arranged on a flexible substrate, then the substrate provides structural support, but the thin films lack the same flexibility causing cracks when bent
Solution Approach 1:
The device separates the structural support function (performed by the flexible substrate) from the thin film components (arranged only on the rigid circuit board portion). This segmentation allows the substrate to provide flexibility and structural support without requiring the thin films to be flexible.
Solution Approach 2:
The flexible substrate acts as an intermediary between the rigid circuit board and the external environment, absorbing mechanical stress and preventing it from being transmitted to the thin films on the circuit board. This intermediary role protects the thin films from stress-induced cracks.
3Ease of operation
If the substrate is made flexible to enable bending, then the device can be curved, but defects such as cracks in inorganic insulation films allow water infiltration and degradation
Solution Approach 1:
The device is segmented into a flexible substrate portion that can be bent and a rigid circuit board portion that houses the thin films. This segmentation ensures that bending operations only affect the substrate portion, while the circuit board portion with thin films remains protected from mechanical stress and water infiltration.
Solution Approach 2:
The flexible substrate's ability to bend is converted into a protective feature by positioning it between the external environment and the thin films. The substrate absorbs mechanical stress and prevents water infiltration to the thin films, transforming the potential harm of flexibility into a protective benefit.
Data Source
AI summary
In a display device using a substrate having flexibility, a drop in reliability due to defects such as cracks in the case where a substrate is made to curve is controlled. A display device is provided including a first substrate having flexibility, the first substrate including a curved part, an organic film covering a first surface of the first substrate and a second surface opposing the first surface in the curved part; and a pixel part and a drive circuit part arranged on the first surface.